发一个脸书电面的面经
SQL:
table 1: useid|sessionid|date|event(open session/end session/scroll down/first click/send message)
table 2: sessionid|date|sessiontime
Q1: what is the average number of sessions per user for the past 30 days
Q2: daily active user for the past 30 days
Product Questions:
add a few feature to marketplace, 怎么决定要不要加这个feature，怎么test